The present invention relates to systems for mounting heatsinks in computers. More particularly, although not exclusively, the present invention relates to methods and apparatus for mounting heatsinks in thermal contact with integrated circuits in computer systems. The invention is particularly suitable for use with microelectronic devices which are generally planar in shape and mounted on a circuit board in a way which would otherwise render it difficult to maintain the device in thermal contact with the heatsink in a secure and reliable fashion.
As a general rule, the reliability and longevity of a semiconductor device is roughly inversely proportional to the square of the junction temperature change. Therefore, an effective increase in the reliability and life of a microelectronic component can be achieved by a relatively small reduction in operating temperature. For high-performance, high value components such as new generation microprocessors this issue may be particularly acute given that the failure and replacement of such a device is usually outside the scope of routine maintenance and abilities which might be expected of a typical PC user. Further, such failures will adversely affect a vendors business as they usually require the return of equipment and extended servicing to say nothing of damaging consumer goodwill and the vendor""s credibility.
Modem microprocessor chips produce a significant amount of heat and it has been observed that the power dissipation of such chips has been increasing faster than the ability of available technology to effectively cool them. Excessive component heating can lead to chip failure and, given the inability of most microelectronic devices to dissipate sufficient heat, it is therefore critical to the function of most modem computers that some form of cooling system is provided.
The process of cooling an electronic component is actually comprised of a number of heat exchange steps. For example, for a heatsink in thermal contact with a microprocessor, heat is conducted away from the chip via a thermal conduction path to a heatsink. Heat is then dissipated from the heatsink by means of a fan mounted thereon. Alternatively, or the heatsink can be placed in the path of forced or convective airflow. This airflow radiates the beat away into the surrounding environment thus indirectly cooling the device on which the heatsink is mounted.
A critical part of the thermal conduction pathway is the thermal junction between the microelectronic device itself and the heatsink. However, heatsinks and microelectronic devices have conflicting physical and thermal characteristics which make them difficult to thermally couple. The heatsink is heavy and large and the microelectronic device is generally smooth, small and has a low profile on its circuit board mount.
To optimize their efficiency, heatsinks are uisually fabricated by die casting, or otherwise fabricating, thermally conductive materials into radiators with large surface areas. To increase the surface area and thus their radiative efficiency, the heatsink can include fins, airfoils and other shapes designed to be amenable to forced convection cooling and sufficient to dissipate large quantities of waste heat.
Further, it is necessary to use physically large heatsinks which often dwarf the device and its support hardware. Being heavy and bulky, heatsinks tend to transmit shock and vibration to the device and the circuit board on which it is mounted. Also, in situations where a fan is attached to provide forced cooling high frequency vibration may be transmitted to the circuit board. This mechanical vibration can cause not only failure of the device, its support mechanism or socket, surrounding motherboard structure and electrical connections to other parts of the circuit. Also, attaching a heavy heatsink to the motherboard can take up significant space on the circuit board due to the presence of attachment or mounting points around the microprocessor
Another problem is that the often-bulky heatsink is mounted over the microprocessor and bolted to attachment points on the motherboard located around the perimeter of the microprocessor. This can cause problems as motherboards are usually made of fairly thin material and simply attaching a heavy heatsink to a motherboard can result in circuit board flex and breakage. This can be worsened by aligning the motherboard vertically such as in a tower computer configuration. In such an orientation, the weight of the heatsink can cause torsional flexing which can crack the motherboard material, disrupt electrical connections and damage the microprocessor. This point may be particularly problematic as it is common to use a thermal bonding paste to attach the heatsink to the microprocessor. Thus any stresses and vibrations caused by the unsupported weight of the heatsink will be transmitted directly to the microprocessor.
It is therefore an object of the invention to provide for a system for mounting a heatsink to a microelectronic device which prevents or at least reduces the risk of damage or failure of a microelectronic device and/or it""s circuit hardware due to vibration, shock and weight induced distortion of the circuit hardware and/or microelectronic device while at the same time ensuring proper thermal conduction between the heatsink and the microelectronic device.
In one aspect the invention provide for a mounting arrangement for a heatsink for cooling a microelectronic device contained within a chassis, the mounting arrangement including:
a heatsink;
a motherboard incorporating the microelectronic device thereon; and
securing means adapted to position both the heatsink and the motherboard in a mounting configuration so that the motherboard is held in fixed relation to the chassis and the heatsink is biased in thermal contact with the microelectronic device by means of a biasing means adapted to engage with both the securing means and the heatsink, whereby the weight of the heatsink thereby is substantially supported by the chassis by way of the securing means.
In an alternative embodiment, the securing means may be attached indirectly to the chassis by means of an extender, panel or similar.
Preferably the heatsink is biased against the microelectronic device by means of resilient means positioned and adapted so that any relative movement between the securing means and the heatsink is cushioned.
The securing means may be in the form of a plurality of pins, each pin having:
a chassis engagement thread at a chassis end thereof
a heatsink engagement means at a heatsink end thereof; and
a motherboard engagement section adapted so as to engage the motherboard so that it is held at a fixed separation from the chassis.
The motherboard is preferably held immediately adjacent the chassis or alternatively, the motherboard is held at a fixed distance from the chassis.
Preferably each pin includes an overhanging lip at the heatsink end which is shaped to engage a coil spring, through which the pin penetrates, in such a way that the location of the heatsink in relation to the microelectronic device is kept substantially constant.
The heatsink is preferably mounted on a plate, the plate having a plurality of apertures, each corresponding to a pin, wherein the pins, in the mounting configuration, penetrate the plate and the motherboard and are fixed to the chassis in such a way that the motherboard is held in a fixed position in relation to the chassis, and the plate, while being free to move on the pins, is biased against the microelectronic device by way of the pins while damping relative movement between the chassis and the heatsink.
In a further aspect of the invention there is provided a pin which adapted for securing a heatsink to a microelectronic device, the pin being in the form of an elongate member having a chassis engagement means at a first end, a heatsink engagement means at a second end and an engagement lip at a point between the first and second end, the elongate member and engagement lip adapted so that the pin can pass through and engage the heatsink at the second end and penetrate and engage with an aperture in a motherboard by means of the lip so as to retain the motherboard in fixed relation to the chassis.
Preferably the pin further includes a biasing means located between the heatsink engagement means and when in use, the heatsink so that when the lip engages with the motherboard aperture, the heatsink and motherboard are held at a substantially fixed separation while any movement between the two is damped by the biasing means.
In an alternative embodiment, the pin may be constructed in a plurality of sections.
The biasing means may be a coil spring.
In a preferred embodiment, the heatsink engagement means may comprises an overhanging lip adapted to engage the heatsink by way of compressing the biasing means wherein the biasing means is interposed between the heatsink or heatsink plate and the lip